The invention relates to a suspension system for a drive assembly of a helicopter of the type utilizing a belt drive arranged between an engine output shaft and a main helicopter rotor.
A drive concept of a helicopter has been contemplated that comprises a first belt drum that is connected with the transmission output shaft and a second belt drum that is connected with an angular gear of the main rotor. A flat belt that surrounds the two drums drives the angular gear located above the engine and thus the main rotor. When the engine is started, the belt is shifted for the disconnecting of the angular momentum from the engine. Then the pilot tightens the belt by means of a device, whereby the rotor is set into rotation.
By the tightening of the belt, the engine is pulled upward and as a result of the simultaneously occurring output torque, it twists around its longitudinal axes in its elastic suspension. As a result, the lower belt drum loses its parallelism with the upper belt drum, and a quiet and wear-resistant movement of the belt is not longer ensured. In order to avoid these disadvantages, rubber metal elements having extremely hard spring rigidities are provided in the case of previously contemplated suspensions for the helicopter engine, having the purpose of carrying the weight and supporting the torque. An additional elastic support that connects the two belt drums with one another has the purpose of ensuring their exact positioning.
The use of bearing elements with an extremely high spring rigidity therefore no longer permit a satisfactory insulation of the vibrations on the side of the engine.
It is an objective of the invention to provide an improved elastic suspension system for a drive assembly of a helicopter that ensures an insulation of the vibrations induced by the engine and nevertheless ensures an exact alignment of the belt drum for a quiet movement of the belt.
According to the invention, this objective is achieved by constructing the bearing system with two spaced bearing in the area of the belt drums and another bearing at the opposite end of the engine, the bearings having their rigidity coordinated such that limited swivel movements of the assembly around the drum axes are facilitated along with lifting movements.
A principal advantage achieved by means of the preferred embodiments of the invention are essentially that, also when soft, well-insulating bearings are used, the parallelism of the belt drums is ensured. The arrangement of the bearings at the engine and the coordination of the rigidities permit only rigid-body movements that do not have any disadvantageous effect on the movement of the belt.
Thus, it is permitted that the engine can swivel around the longitudinal axes of the two belt drums, and a parallel lifting movement of the assembly is possible to a limited degree. What is prevented, however, is a twisting of the engine around its transverse axes (pitch) and around its vertical axes (yaw) as well as an axial shifting in the direction of the crankshaft.
Between the two belt drums, an additional support may be provided that absorbs the belt tension and that, in the case of different load conditions, aligns the belt drums in parallel to one another, according to certain preferred embodiments. If the output shaft is reinforced, embodiments are also contemplated where such support is left out.